1. Field of the Invention
The present invention relates to a method of adjusting an output level of a measurement pixel, a color sensor, and a virtual slide apparatus.
Priority is claimed on Japanese Patent Application No. 2011-007138, filed Jan. 17, 2011, the content of which is incorporated herein by reference.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
To accurately detect spectral information of a subject, a photographing wavelength band needs to be divided into more channels. Further, a color sensor is used to obtain the spectral information of the subject. For example, a reading circuit disclosed in Japanese Unexamined Patent Application, First Publication No. 2006-349623 is known as a reading circuit used for the color sensor. In the following description and drawings, like elements are respectively denoted by like reference numerals.
FIG. 18 is a schematic diagram illustrating a configuration of a known color sensor. In the shown example, a color sensor 200 includes pixel and reading circuits B10-1 to B10-6, gain circuits B20-1 to B20-6, integration time calculation units 38-1 to 38-6, gain calculation units 39-1 to 39-6, and a driving control circuit 310. Further, the pixel and reading circuits B10-1 to B10-6 include pixels 31-1 to 31-6 for detecting spectral information of a subject in respective divided wavelength transmission bands, reference voltage terminals 32-1 to 32-6, switch elements 33-1 to 33-6, capacitive elements 34-1 to 34-6, and operational amplifiers 35-1 to 35-6. Further, sections including the reference voltage terminals 32-1 to 32-6, the switch elements 33-1 to 33-6, the capacitive elements 34-1 to 34-6, and the operational amplifiers 35-1 to 35-6 are referred to as reading circuits 30-1 to 30-6.
In the shown example, the pixels 31-1 to 31-6 included in the pixel and reading circuits B10-1 to B10-6 detect any of six colors: purple, blue, green, yellow, red and orange. Specifically, the pixel 31-1 included in the pixel and reading circuit B10-1 is a pixel for detecting violet light. Further, the pixel 31-2 included in the pixel and reading circuit B10-2 is a pixel for detecting blue light. Further, the pixel 31-3 included in the pixel and reading circuit B10-3 is a pixel for detecting green light. Further, the pixel 31-4 included in the pixel and reading circuit B10-4 is a pixel for detecting yellow light. Further, the pixel 31-5 included in the pixel and reading circuit B10-5 detects red light. Further, the pixel 31-6 included in the pixel and reading circuit B10-6 detects orange light.
In the color sensor 200, light from the subject is incident on the pixels 31-1 to 31-6. The switch elements 33-1 to 33-6 control integration times based on reference voltages applied to the reference voltage terminals 32-1 to 32-6. The capacitive elements 34-1 to 34-6 perform integration to obtain voltage changes according to photocurrent, and output the voltage changes to the output terminals of the operational amplifiers 35-1 to 35-6.
In the color sensor 200, the gain circuits B20-1 to B20-6 amplify and read output changes of the output terminals of the operational amplifiers 35-1 to 35-6. The integration time calculation units 38-1 to 38-6 calculate respective integration times of the pixel and reading circuits B10-1 to B10-6 based on information sent from the driving control circuit 310. The gain calculation units 39-1 to 39-6 calculate respective gains of the gain circuits B20-1 to B20-6 based on information sent from the driving control circuit 310. Using the integration times and the gains set by the integration time calculation units 38-1 to 38-6 and the gain calculation units 39-1 to 39-6, output signals are output from the output terminals 37-1 to 37-6.
Further, voltages Vout output from the output terminals 37-1 to 37-6 may be represented by Equation (1), in which the reference voltage is Vref, the photocurrent generated in the pixels 31-1 to 31-6 is IPD, the time for which the photocurrent IPD is integrated by opening the switch elements 33-1 to 33-6 is TINT, the capacitance of the capacitive elements 34-1 to 34-6 is C, and the gain of the gain circuits B20-1 to B20-6 is G.
                              V          out                =                              V            ref                    +                      G            ·                                                            I                  PD                                ⁢                                  T                  INT                                            C                                                          (        1        )            
FIG. 19 is a graph illustrating an example of output levels of signals output from the output terminals 37-1 to 37-6 when integration times of the outputs of the pixels 31-1 to 31-6 for detecting light of any of the six colors are changed to an integer multiple of a reference integration time in a method disclosed in Japanese Unexamined Patent Application, First Publication No. 2006-349623. A vertical axis of the shown graph indicates output levels of signals based on output signals of the pixels 31-1 to 31-6, which are output from the output terminals 37-1 to 37-6. If the output level of the signal is equal to or higher than the noise level, and equal to or lower than a saturation level, the signal can be used when the spectral information is acquired. The noise level is a low output level that cannot be discriminated from noise. Further, the saturation level is a high output level exceeding the capacitance of the capacitive element included in the color sensor. Hereinafter, an output level equal to or higher than the noise level and equal to or lower than a saturation level is described as a valid level. Further, a horizontal axis of the shown graph indicates the output terminals 37-1 to 37-6 that output the signals based on the output signals of the pixels 31-1 to 31-6 in the first to sixth read-outs.
Specifically, (1) on a horizontal axis indicates the output terminal 37-1 that outputs the signal based on the output signal of the pixel 31-1 for detecting violet light in the first to sixth read-outs, and a value on the vertical axis corresponding to the horizontal axis (1) indicates the output level of the signal output from the output terminal 37-1. Further, (2) on the horizontal axis indicates the output terminal 37-2 that outputs the signal based on the output signal of the pixel 31-2 for detecting blue light in the first to sixth read-outs, and a value on the vertical axis corresponding to the horizontal axis (2) indicates the output level of the signal output from the output terminal 37-2. Further, (3) on the horizontal axis indicates the output terminal 37-3 that outputs the signal based on the output signal of the pixel 31-3 for detecting green light in the first to sixth read-outs, and a value on the vertical axis corresponding to the horizontal axis (3) indicates the output level of the signal output from the output terminal 37-3. Further, (4) on the horizontal axis indicates the output terminal 37-4 that outputs the signal based on the output signal of the pixel 31-4 for detecting yellow light in the first to sixth read-outs, and a value on the vertical axis corresponding to the horizontal axis (4) indicates the output level of the signal output from the output terminal 37-4. Further, (5) on the horizontal axis indicates the output terminal 37-5 that outputs the signal based on the output signal of the pixel 31-5 for detecting red light in the first to sixth read-outs, and a value on the vertical axis corresponding to the horizontal axis (5) indicates the output level of the signal output from the output terminal 37-5. Further, (6) on the horizontal axis indicates the output terminal 37-6 that outputs the signal based on the output signal of the pixel 31-6 for detecting orange light in the first to sixth read-outs, and a value on the vertical axis corresponding to the horizontal axis (6) indicates the output level of the signal output from the output terminal 37-6.
Further, in the shown example, the integration time in the first read-out is six times a reference integration time. Further, the integration time in the second read-out is five times the reference integration time. Further, the integration time in the third read-out is four times the reference integration time. Further, the integration time in the fourth read-out is three times the reference integration time. Further, the integration time in the fifth read-out is two times the reference integration time. Further, the integration time in the sixth read is equal to the reference integration time.
Thus, the integration times of the output signals of respective pixels 31-1 to 31-6 are changed to be integer multiples of the reference integration time and the output levels based on the output signals of the pixels 31-1 to 31-6 are read multiple times, such that the output levels based on the output signals of all the pixels 31-1 to 31-6 can be acquired as valid levels. In the shown example, the output level of the signal based on the output signal of the pixel 31-1, which is output from the output terminal 37-1, is read six times to acquire a valid output level. The output levels of the other output terminals 37-2 to 37-6 are read as shown. Further, in the graph, invalid output levels are indicated by a mark x.
However, in the method disclosed in Japanese Unexamined Patent Application, First Publication No. 2006-349623, since integration times of the output signals of the respective pixels 31-1 to 31-6 are changed to be integer multiples of the reference integration time and the output levels based on the output signals of the pixels 31-1 to 31-6 are read multiple times, invalid output levels are generated as shown by the mark x in FIG. 19. Thereby, in acquiring the output levels based on the output signals of all the pixels 31-1 to 31-6 as valid levels, invalid reads occur and the output levels need to be read multiple times, which increases an acquisition time.